The present invention relates generally to mechanical positioning systems, and more specifically to linear slides and planar X-Y positioning mechanisms having essentially no backlash.
An important function of many of even the most basic mechanical devices is to move an item or mechanical element in a controlled manner. In many mechanical applications it is necessary to shift the position of an item in two-dimensional space, i.e. planar motion. The mechanical systems for accomplishing this task have commonly taken the form of slides, flexures, and multi-axis actuators of various types.
Historically, slides, flexures, and actuators are stacked on top of one another in order to move objects in multiple directions. For example, in a common X-Y stage, the Y-axis (e.g., xe2x80x9cfront-to-backxe2x80x9d) slide is carried on top of the X-axis (left-to-right) slide, providing independent, orthogonal two-dimensional motion in the X-Y plane. Typically, the drivers to move the slides mainly comprise a motor connected to a screw for converting rotary motion into linear displacement. The motor and screw effectuate rotational motion, with the pitch or lead of the screw being transformed into translational motion, which then is imparted to a slide element that moves to-and-fro upon associated guideways.
Conventional lead screw drives suffer from backlash upon reversal, resulting in reduced accuracy. Stacking one linear slide on top of the other can also reduce accuracy because the stacked structure is less compact, and, hence, less rigid.
Rapid progress currently is being made in the field of micro electro-mechanical systems (MEMS), where mechanical operations are performed by minutely sized machines. In current state of the art MEMS devices, drivers and actuators are generally planar elements. Single-axis (e.g. unidirectional) xe2x80x9ccombxe2x80x9d slides have been successfully fabricated with MEMS technology. A need remains, however, for a simple, planar X-Y stage fabricated with MEMS technology that provides positioning capability in two independent directions.
Against this background, the present invention was developed.
The invention relates to a planar apparatus for accurately positioning a movable platform in one or two dimensions. A sample or workpiece can be placed on top of the platform. A pair of master and slave disks engage opposing sides of the movable platform. Rotational driving means, such as geared motors, are connected to each disk at a location offset from the disk centers, so that the disks rotate eccentrically about the driver""s axes of rotation. The pair of master and slave disks rotate in a coordinated fashion in the same direction. As the master disk rotates eccentrically, the distance between the axis of rotation and the platform""s edge decreases. Simultaneously, the distance between the axis of rotation of the corresponding slave disk and the opposite edge of the platform increases by the same amount. The coordinated eccentric motion of the pairs of master/slave disks compels linear motion of the platform along an axis that is oriented parallel to a line connecting the two disk""s axes of rotation. Smooth coordination of the pair of rotating master/slave disks eliminates backlash by keeping the disks in nearly continuous contact with the platform during movement. Coordination can be achieved, for example, by use of a timing belt, or by electronic synchronization of stepper motors.
Two-dimensional motion of the platform can be achieved by providing two pairs of coordinated master/slave disks, with each pair independently driving orthogonal X-axis and Y-axis motion. This arrangement provides all possible translational motion of the platform in a two-dimensional plane. The two pairs of coordinated master/slave disks can be placed on a single plane, thereby creating a planar X-Y stage. This planar geometry eliminates the need to stack the drive mechanisms on top of each other, making it well suited for MEMS applications. The maximum linear range of motion (e.g. stroke) along a single axis is equal to the largest radial distance from the disk""s axis of rotation to its circumference.